Generally, mammals such as humans have a constant intracranial volume of blood and, therefore, a constant intracranial pressure (“ICP”). A variety of normal and pathological conditions, however, can produce changes in intracranial pressure. Elevated intracranial pressure can reduce blood flow to the brain and in some cases can cause the brain to become mechanically compressed, and ultimately herniate. The most common cause of elevated intracranial pressure is head trauma. Additional causes of elevated intracranial pressure include, but are not limited to shaken-baby syndrome, epidural hematoma, subdural hematoma, brain hemorrhage, meningitis, encephalitis, lead poisoning, Reye's syndrome, hypervitaminosis A, diabetic ketoacidosis, water intoxication, brain tumors, other masses or blood clots in the cranial cavity, brain abscesses, stroke, ADEM (“acute disseminated encephalomyelitis”), metabolic disorders, hydrocephalus, and dural sinus and venous thrombosis. Because changes in intracranial pressure require constant monitoring and possible surgical intervention, the development of techniques to monitor intracranial pressure remains an important goal in medicine. U.S. Pat. No. 6,875,176.
Conventional intracranial pressure monitoring devices include: epidural catheters; subarachnoid bolt/screws; ventriculostomy catheters; and fiberoptic catheters. All of these methods and systems are invasive, and require invasive surgical procedures by highly trained neurosurgeons. Moreover, none of these techniques are suited to rapid or regular monitoring of intracranial pressure. In addition, all of these conventional techniques measure ICP locally, and presumptions are made that the local ICP reflects the whole brain ICP. The teachings of U.S. Pat. No. 6,875,176 illustrate these limitations of the existing methods.
There are no widely accepted methods of non-invasively measuring ICP. Clinically, however, the development of an effective means of measuring ICP is very important as ICP can be predictive of clinical outcome, and can lead to altered, more effective therapy. For example, after traumatic brain injury, intracranial pressure tends to rise requiring both prompt recognition and treatment. Zanier et al. Critical Care 11:R7 (“2007”). The existing standards in measuring ICP require direct, invasive measurement involving the placement of epidural transducers or intraventricular or intraparenchymatous catheters. Frank et al. Zentralbl Neurochir 61(“4”):177-80 (“2000”). The use of invasive methods increases the risk of injury from infection, bleeding or surgical mishap. Czosnyka et al. J. Neurol. Neurosurg. Psychiatry 75: 813-821 (“2004”).
A variety of different techniques for noninvasively measuring ICP have been explored, including, measuring otoacoustic emissions (“Frank et al. Zentralbl Neurochir 61(“4”): 177-80 (“2000”)”), and ultrasound with a transcranial Doppler (Ragauskas et al. Innovative non-invasive method for absolute intracranial pressure measurement [online], [retrieved on Jul. 30, 2008]. Retrieved from the Internet <URL: http://www.neurosonology.org/bern2002/abs—12.html>).
For example, U.S. Pat. No. 6,702,743 (“the '743 patent”) discloses a non-invasive means of measuring ICP. An ultrasound probe is placed on the head of a patient, and is then used to generate an ultrasound pulse which propagates through the skull and brain of the patient. The ultrasound pulse is reflected off of the skull and soft tissue lying in a path perpendicular to the ultrasound probe. A portion of a generated Echo EG signal is then selected, and the Echo EG signal is integrated over the selected portion to generate an echopulsograph (“EPG”) signal. However, in order to determine ICP using the methods of the '743 patent, the operator must manually select, or “gate” a portion of the EPG and then review the EPG waveforms at each gate to determine which provides the optimal EPG waveform for a site of interest in the brain.
We have developed a novel method to noninvasively measure ICP and more generally brain elasticity that requires no manual review of EPG waves by a technician. ICP is determined using an algorithm coupled on a simulated artificial neural network (“SANN”) that calculates ICP based on a determination of a set of interacted ultrasound signals (“IUSs”) generated from multiple ultrasound pulses. The methods and systems of the present invention are capable of rapidly determining ICP without manual review of EPG waves.